The present invention generally relates to a vehicle data communication system and, more particularly relates to a data communication protocol for communicating binary data between electronic devices on a data bus in a vehicle.
Modern automotive vehicles generally include various control systems with electronic devices for controlling vehicle related operations. For example, vehicles are commonly equipped with an engine control module (ECM) generally for controlling engine related operations. In addition, vehicles commonly include control systems configured about the cockpit of the vehicle, and are commonly referred to as cockpit electronics. Cockpit electronics typically include an instrument panel cluster, a driver information system, an electronic radio, a heating, ventilation, and air condition (HVAC) system, and a bead-up display (HUD). At least some of the aforementioned control systems are commonly interconnected by way of a serial data bus for communicating data between the various control systems. The serial data bus typically includes a data line for transmitting serial data bits, as well as a ground line for providing a common ground reference, and a common power line which feeds each of the control system devices to provide electrical power thereto.
Conventionally, the various control systems on a vehicle communicated via the serial data bus by way of a pulse width modulation (PWM) coding, in which each data bit is encoded, and subsequently decoded by sampling the bit at the halfway point. If the voltage level is positive, then the data bit is decoded as a binary "1" value, otherwise the data bit is decoded as a binary "0" value. According to the conventional pulse width modulation coding approach, two voltage pulse edges are generally required to define each bit of data. This approach requires a relatively large number of voltage pulse edges for coding, which can adversely contribute to RF emissions (e.g., noise).
More recently, another encoding approach, referred to as variable pulse width (VPW), has been commercially employed with the SAE J1850 Class II communication bus for use on automotive vehicles. According to the variable pulse width data coding approach, a binary "1" value is assigned to a short high pulse or a long low pulse, while a binary "0" value is assigned to a long high pulse or a short low pulse, respectively. According to the variable pulse width coding approach, only one edge is required to define one bit of data, which thus reduces RF emissions as compared to the pulse width modulation approach.
While the pulse width modulation and variable pulse width approaches have offered suitable data communication in an automotive vehicle, such approaches do not minimize cost and RF emissions. There exists the desirability to minimize the number of voltage pulse edges that are required to define each bit of data for communication between control systems on a vehicle bus. In addition, there exists a need to provide for a fast data bit rate, while reducing the cost per node. Yet, it is also desirable to allow for vehicle data communication which may accommodate less expensive data communication timing devices.
It is, therefore one object of the present invention to provide for enhanced vehicle communication protocol for communicating data on a serial data bus of a vehicle. It is another object of the present invention to provide for fast data bit rates with reduced emissions. It is a further object of the present invention to provide for a reduced cost vehicle communication system, particularly for components employed at each node in the vehicle. It is yet another object of the present invention to provide for priority message arbitration which allows for a master-less bus arrangement.